Chemical Vapor Deposition Reactor Research Articles

Large Area Growth and Phase Selectivity of MoTe2 Nanosheets through Simulation‐Guided CVD Tellurization

AbstractAmong transition metal dichalcogenides, molybdenum ditelluride (MoTe2) holds significant attention due to its polymorphic nature including semiconducting, metallic, and topological semimetal phases. Considerable efforts are devoted to synthesizing MoTe2 nanosheets to make them suitable for device integration in nanotechnologies and for fundamental investigations. In this respect, chemical vapor deposition (CVD) via tellurization of a pre‐deposited Mo thin film is an easy and flexible way for synthesizing large scale MoTe2 nanosheets. Here, the study report on the CVD of large‐area (up to 4 cm × 1 cm) MoTe2 nanosheets with pure 1T’ and 2H phase selection by design. Within the tellurization scheme, the vapor‐solid reaction between the pre‐deposited molybdenum film and tellurium vapor is studied thus optimizing the scalability and quality of the MoTe2 nanosheets grown on SiO2/Si substrates. It is demonstrated that the MoTe2 structure and morphology are kinetically dictated by the tellurium concentration gradient on the reaction site with varying geometric configurations inside the CVD reactor. This study provides a pivot scheme for enabling scalable 1T’ and 2H‐MoTe2 integration in applications for novel micro‐ and nano‐electronics, spintronics, photonics, and thermoelectric devices.

Improved adaptive backstepping control of MPCVD reactor systems with non-parametric uncertainties

This paper presents an improved adaptive backstepping control strategy for a microwave plasma chemical vapor deposition (MPCVD) reactor system. To describe the dynamics of the reactor system, a non-parametric uncertain nonlinear system model with unknown control direction functions is built up. In order to deal with the non-parametric uncertainties of the system, direct adaptive laws are primarily proposed to estimate such uncertainties, which is superior to traditional adaptive backstepping that can only address parametric uncertainties. Moreover, an equivalence transformation of the system is given to address the system unknown control direction functions. By using Lyapunov stability criterion, it can be proved that the target signals (desired temperature, desired pressure, and desired gas flow rates) are tracked by the reactor system outputs with small errors. Finally, simulation results are given to demonstrate the effectiveness of the proposed control method.

(Digital Presentation) Properties of Selectively Grown Si:P Layers below 500°C for Use in Stacked Nanosheet Devices

With the introduction of novel stacked CMOS transistor integration schemes such as sequential 3D and CFETs [1,2], there is an increasing need for highly active source/drain layers with a low overall thermal budget. For some integration schemes, processing temperatures below ~ 525°C are desired [3] and in most cases, the contacts need to be formed on the {110} surfaces of exposed Si nanosheets. In this paper, we report on selectively grown Si:P layers below 500°C targeting application in stacked nanosheet-based devices. In contrast to conventional approaches where selectivity is obtained at low temperatures using Cyclic-Deposition and Etch (CDE) with HCl/GeH4 as an etchant [4,5], we rely for this work on Cl2-based etching in combination with Si3H8 as a high-order Si precursor [6]. The Si:P layers were grown in a 300 mm ASM Intrepid® ES reduced pressure chemical vapor deposition reactor on Si (001) substrates.Figure 1 shows some typical characteristics for the Si:P layers without etching (“Dep-only”) and CDE Si:P layers below 500°C. As the temperature is lowered, the growth rate and P incorporation for a given PH3 flow decreases substantially, while the active concentration increases. For both the “Dep-only” and CDE layers, a minimum develops in the resistivity which corresponds to a maximum in active concentration as derived from micro-Hall measurements. Due to the etching during CDE, a P-enrichment takes place and the P concentration in the layers is enhanced compared to the “Dep-only” case. A minimum resistivity of 0.28 mOhm.cm (Pact ~ 6e20/cm3) is obtained for CDE at 480°C which is slightly larger than the minimum resistivity of 0.24 mOhm.cm (Pact ~ 1e21/cm3) for the “Dep-only” case at the corresponding temperature.Figure 2 shows the application of the CDE process on wafers with fins. By lowering the deposition time at a constant etching time per cycle, a (wafer-scale) selective regime can be reached. For the “Dep-only” case, quite some defects and nuclei are present on the sidewalls of the Si-fins and the oxide dielectric, respectively, which are finally removed by sufficient Cl2 etching.Figure 3 compares the corresponding X-TEMs of the above fins after “Dep-only” and selective CDE conditions. For the “Dep-only” case we can only observe a mono-crystalline growth in the <100> direction. For other growth directions like <110>, epitaxial breakdown-down occurs resulting in a substantially reduced crystalline thickness. With the use of Cl2 based CDE, a selective growth can be reached as well as a clear structural improvement in the <110> growth direction, which is very important for the application in nanosheet devices. Finally, once a (111) facet is formed, twin defects occur as expected for low temperature Si:P and Si:C:P [7].The growth behavior of the CDE processes in relevant nanosheet geometries is currently under investigation.

Low Temperature Selective Epitaxy of Group-IV Semiconductors for Nanoelectronics

Continuous improvement of device performance is becoming very challenging as the transistor dimension approaches the physical limits of scalability. In particular, the source/drain (S/D) layer resistivity and contact resistance at the S/D region became major components for further parasitic resistance reduction [1]. Therefore, layers with high active doping concertation is required for future technology nodes. From another side, novel architectures such as 3D-stacked devices constraints the allowed thermal budget for epitaxy processes [2]. In this work, we will review our recent achievements on LT epitaxy for both Si:P and SiGe:B layers to enable (i) parasitic resistance reduction and (ii) novel integration schemes.All layers were grown in a 300 mm ASM reduced pressure chemical vapor deposition reactor on Si(001) substrates and patterned substrates.Firstly, we will discuss the benefits of SiP growth at low temperature leading to high active doping concentrations (~1.1×1021 cm-3), as reported in our previous work [3]. Figure 1 shows the omega-2theta scans around the symmetric (004) reflections of the Si:P/Si stacks. As expected, reducing the Si precursor flow leads to a higher substitutional P (~7.5%) incorporation in the layer. The good crystallinity of the SiP layer is attested by the well-defined thickness fringes. Figure 2a represents the XRR scans of non-selective SiP process and selective SiP process compared to 100 nm bare SiO2 on Si substrate. The presence of fringes (red curve) indicates that a 2D amorphous SiP layer is deposited on SiO2. To confirm the full selectivity of the process and the absence of nuclei on the SiO2 surface, top view SEM was performed (cf. Figure 2b).Afterwards, we will focus on the SiGe:B epitaxy at low temperature. Figure 3a shows omega-2theta scans around the symmetric (004) reflections of the SiGe:B/Si stacks for various B flows. The apparent Ge content drops from 52.1% to around 41.3% when B flow was multiplied by 16. The inset represents the reciprocal space map (RSM) around the asymmetric (224) peak of SiGe:B layers grown on Si(001) substrates with the highest B flow. The RSM clearly indicates high quality and fully strained SiGe:B layer. Figure 3b depicts the apparent Ge drop vs B flow. This reduction in Ge content is attributed to B strain compensation effect leading to artificially lower Ge content [4]. Figure 3c represents SiGe:B layer resistivity vs B flow. Resistivity drops until a critical B flow and then increases with increasing B flow. Figure 4 shows active doping concentration and Hall mobility as function of the B flow. The Hall measurements were performed on a cleaved wafer edge and assume a Hall scattering factor of 1. Active carrier concertation increases with increased B flow. As a side effect of the higher activation, the Hall mobility is lowered likely due to an increase in ionized impurity scattering which is the reason why the resistivity does not decrease substantially below a certain value for higher B flows at current growth conditions. Layers with similar physical properties have resulted in S/D metal contact resistivity of ~5×10-10 Ohm.cm2 [5]. Figure 5 depicts the selective process on advanced patterned nanosheet test structures. Figure 5a illustrates the selectivity towards several nanosheet structures, Figure 5b shows a zoomed in image indicating selective process towards inner SiN spacers and SiO2. Figure 5c is a FFT of the SiGe:B area indicated by red square and Figure 5d is an EDS map of the key elements (Si, Ge, O, C, Cl, F, N). Figure 6a and 6b show the selective process stability over 20 runs. The HR-XRD measurements at wafer center are represented in Figure 6a. Figure 6b represents the resistivity at the wafer center. Thickness uniformity across one of the wafer is illustrated in Figure 6c. The results indicate excellent wafer to wafer and within wafer uniformities despite low temperature processing.LT epitaxy offers several advantages to reach high active doping concentrations and enable novel integration schemes. Despite challenges associated to LT epitaxy, in this work we showed the possibility to grow selective layers while maintaining the excellent physical layer properties, within wafer uniformity and wafer to wafer reproducibility.[1] H. Wu et al. EEE International Electron Devices Meeting (IEDM), (2018), pp. 35.4.1.[2] A. Vandooren et al. IEEE Symposium on VLSI Technology, (2018), pp. 69-70.[3] R. Khazaka et al. ECS Meeting s, MA2020-02(24), (2020) 1734-1734.[4] J.M. Hartmann et al. ECS JSST, 3(11) (2014) 382.[5] H. Xu et al. IEEE Symposium on VLSI Technology, (2022), (to be published). Figure 1

(Si)GeSn Isothermal Multilayer Growth for Specific Applications Using GeH4 and Ge2H6

The experimental demonstration of Ge1-xSnx alloys lasers opened group-IV materials towards high-performance electronic and photonic devices that can be easily integrated with the current Si semiconductor technology. In recent years, GeSn-based optoelectronic devices including light-emitting and detectors, modulators, and CMOS have been proven.The major challenges for the Ge1-xSnx epitaxy arise from the low solid solubility of Sn in Ge, the large lattice mismatch, and the reduced thermal stability between Ge and Sn. All these are becoming extremely critical at higher Sn contents. Non-equilibrium conditions offered by molecular beam epitaxy (MBE), chemical vapor deposition (CVD), flash lamp, or laser annealing have been lately investigated. Between them, CVD is to date the preferred growth technique for its current development compatible with the industry offering micron-thick layers with the highest crystal quality.While Tin-tetrachloride (SnCl4) becomes the standard Sn precursor, for Ge different gasses, like germane (GeH4) and digermane (Ge2H6) are used attempting to archive high Sn incorporation and high material quality. While Ge1-xSnx films with the same high Sn content can be obtained regardless of the used precursor, the advantages and disadvantages of each precursor are discussed in this work. The use of Ge2H6 is accompanied by high growth rates, being favorable in applications where relatively thick films are needed, such as laser structures. On the other hand, with a relatively low growth rate, GeH4 provides a greater thickness control, achieving clear and sharp interfaces in heterostructures. For this reason, GeH4 is the appropriate precursor for quantum transport or spintronic.The biggest challenge in heterostructure designs is going up and down in Sn content. The growth of a Ge1-ySny on a Ge1-xSnx, y<x, or SiGeSn layer cannot be performed by increasing the growth temperature. Post-annealing processes lead to strong crystallinity degradation of the already grown layer by strong Sn diffusion or Sn segregation due to the limited thermal stability of Ge1-xSnx alloys.In this work, we address simple methodologies to enhance the gradient or step Sn content without changing the process temperature. Controlling only the carrier gas flow while keeping the standard growth parameters constant, high-quality Ge1-xSnx alloys with uniform Sn content up to 15 at.% are obtained. The proposed method acts as guidance to produce Ge1-xSnx heterostructures that can be extended to any CVD reactor, independently of the used precursor, GeH4 or Ge2H6. Different devices structures are presented proving the applicability of the isothermal multilayer growth. Figure 1

High Performance Planar Antimony-Based Superlattice Photodetectors Using Zinc Diffusion Grown by MBE

In this letter, we report a mid-wavelength infrared (MWIR) planar photodetector based on InAs/InAs1−xSbx type-II superlattices (T2SLs) that has a cut-off wavelength of 4.3 μm at 77 K. The superlattice for the device was grown by molecular beam epitaxy while the planar device structure was achieved by Zinc diffusion process in a metal–organic chemical vapor deposition reactor. At 77 K, the peak responsivity and the corresponding quantum efficiency had the value of 1.42 A/W and 48% respectively at 3.7 μm under −20 mV for the MWIR planar photodetector. At 77 K, the MWIR planar photodetector exhibits a dark current density of 2.0 × 10−5 A/cm2 and the R0A value of ~3.0 × 102 Ω∙cm2 under −20 mV, which yielded a specific detectivity of 4.0 × 1011 cm·Hz1/2/W at 3.7 μm. At 150 K, the planar device showed a dark current density of 6.4 × 10−5 A/cm2 and a quantum efficiency of 49% at ~3.7 μm under −20 mV, which yielded a specific detectivity of 2.0 × 1011 cm·Hz1/2/W.

Numerical simulation of carbon nanotube fibers motion in the chemical vapor deposition reactor

In order to explore the motion of carbon nanotube fibers prepared by the chemical vapor deposition reactor, the gas flow field in the reactor is simulated using the computational fluid dynamics software. The dynamics analysis of carbon nanotube fibers in the gas flow field is carried out based on the bead-rod fiber model. The fiber motion is simulated numerically by introducing the gas velocity into the fiber dynamics equation. Through iterative computation, the instantaneous motion state and trajectory of carbon nanotube fibers in the reactor are obtained. The simulation results are consistent with the motion diffraction photo of carbon nanotube fibers and explain the cause of ‘sock’ structure in the preparation process of carbon nanotube fibers preliminary. The results show the great potential of this research for understanding the forming mechanism of carbon nanotube fibers.

Remarkable enhancement in CNT fiber synthesis by reducing convection vortex in floating catalyst chemical vapour deposition

Synthesis of carbon nanotube fiber (CNT fiber) in a floating-catalyst chemical vapor deposition (FC-CVD) reactor suffers from very low carbon efficiency and yield. One of the major causes of poor conversion is the formation of internal convection vortex near the inlet, where catalyst particles undergo agglomeration and deactivation resulting in a significant reduction in the yield. It also lowers the average aspect ratio of the CNTs. In this work, a novel method of using an internal heating rod has been employed to reduce the convection vortex by altering the temperature gradient locally. The optimum position, temperature and size of the heating rod have been determined by computational fluid dynamics (CFD) for enhanced carbon conversion. The yield and the aspect ratio of CNT fiber, synthesized at the optimized condition have enhanced by 90% and 50%, respectively while the average ratio of D to G peak in Raman spectra (ID/IG) has reduced by 58%. For the first time, residence time distribution (RTD) analysis has been used to describe the effect of convection vortex on carbon conversion for the synthesis of CNT fiber. This work demonstrates simultaneous enhancement in yield, crystallinity and aspect ratio of the CNT fiber by reducing the convection vortex.

Forecasting carbon nanotube diameter in floating catalyst chemical vapor deposition

Carbon nanotube (CNT) diameter control is essential for many conductive and structural applications; to date, a general diameter methodology applicable to all floating catalyst chemical vapor deposition (FC-CVD) reactors is not yet established. Single-walled CNT (SWCNT) diameter was robustly controlled by systematically exploring an extensive variety of fundamental FC-CVD reactor parameters (631 experiments) including: CO2, H2, and Ar flowrates; fuel flowrate; added H2O (up to an unprecedented 30% of fuel by mass); ferrocene concentration; reactor temperature (covering temperatures with solid and liquid floating catalyst); and quartz reactor tube age. As a function of these experimental input factors, across three Raman wavelengths, validated statistical models robustly predicted: 1) diameter of SWCNTs, via the weighted average of the radial breathing modes (RBMs); 2) the conditions which led to SWCNT growth, via the categorical appearance of viable RBMs. This is noteworthy because it illustrates a new paradigm of FC-CVD reactor control, accounting for interaction between reactor input factors, system noise, and other non-linear responses. Oxidative influences (including laboratory humidity) yield smaller CNT diameters, although H2O becomes important only at higher temperatures and CO2 is countered by H2 addition. Increasing reactor temperature increased diameters. Pyrolysis calculations showed species inside the reactor differ substantially from species injected. A kinetic-thermodynamic model of catalyst particle size and chemical state revealed that adding oxidative species kept the active catalyst particles small, explaining the resulting small CNT diameters. The powerful combination of our multivariate statistical approach with kinetic-thermodynamic modeling enables unprecedented insight and control over CNT synthesis.

Ti3SiC2-SiC multilayer thin films deposited by high temperature reactive chemical vapor deposition

Ti3SiC2-SiC multilayer film coatings synthesis was investigated with the high temperature reactive chemical vapor deposition technique. The method consists of a reaction between SiC (as the substrate and interlayers) and H2-TiClx gaseous mixture. Cross-section morphologies and phases were studies by scanning electron microscopy (SEM), X-ray diffraction (XRD) and automated crystal orientation mapping in transmission electron microscopy (ACOM-TEM). Thermodynamic calculations were carried out to select more appropriate gas composition for reactor conditions and understand the chemistries of reaction between layers in the different steps. Nano and Vickers micro-indentation mechanical tests determined hardness and elastic modulus of the Ti3SiC2 and Ti5Si3Cx surfaces samples. Oxidation tests and emissivity measurements allowed the evaluation of Ti3SiC2-SiC coatings as materials for high temperature applications. The multilayered systems kept their mechanical integrity and showed low degradation after 25 h of thermal cycles at 900 °C in air. The measurement of the optical properties also revealed an increase of the absorptivity after the oxidation of Ti3SiC2 surface sample.

In-situ synthesis of graphene encapsulated Fe/Fe2O3 nanoparticles for possible biomedical applications

This paper reports on the in-situ synthesis, optimization, characterization and cytotoxicity tests of multi-layer graphene (MLG) encapsulated Fe/Fe2O3 nanoparticles (Fe/Fe2O3@C core–shell nanostructures) by spray drying-assisted chemical vapor deposition (CVD) using iron-nitrate/silica-based precursors. The influences of CVD reaction temperature, holding time, CH4/H2 gas flows and pressure on the synthesis of MLG encapsulated Fe/Fe2O3 nanoparticles were investigated. CVD-synthesized powders were purified using acid leaching to remove residual silica and probable uncoated Fe/Fe-oxide phases. XRD analyses revealed the presence of FCC (Fe,C), BCC Fe, graphite/graphene and trace amount of Fe2O3 phases. Raman spectra confirmed the existence of MLG shells. TEM indicated that MLG (from at least 3 to maximum of 35 layers) wrapped around the metallic cores ranged between 4 and 85 nm. Purification of nanoparticles did not degrade, dissolve or create discontinuity on the MLG structure. VSM measurements showed that nanoparticles obtained from the optimized conditions (900 °C, 100 ml/min CH4/H2, 50 mbar) had a soft ferromagnetic behavior with low saturation magnetization (∼85 emu/g) and coercivity (∼552 Oe) values. Optimized MLG encapsulated Fe/Fe2O3 nanoparticles were successfully suspended in water using a poly(acrylic acid) coating. Aqueous MLG encapsulated Fe/Fe2O3 nanoparticles were cytocompatible below 100 μg/ml at short incubation times, and showed the potential to be used in biomedical applications.

An efficient chemistry-enhanced CFD model for the investigation of the rate-limiting mechanisms in industrial Chemical Vapor Deposition reactors

An efficient CFD model for the deposition of alumina from a gas mixture consisting of AlCl3, CO2, HCl, H2 and H2S in an industrial CVD reactor with multiple disks and a rotating feeding tube, is proposed. The goal is twofold: (i) to predict the thickness of the deposited material, (ii) to investigate whether the process rate is determined by the reaction rate or by diffusion. A reaction model that consists of a gas-phase homogeneous reaction and a heterogeneous reaction is implemented, with a proposed kinetics rate that includes the effect of the H2S concentration. The latter has a catalytic effect, but the mechanism is not entirely understood. The entire reactor geometry (consisting of 40–50 perforated disks) is divided into appropriately chosen 7-disk sections. The 2D, time-dependent CFD model is validated using production data for the deposition thickness. The proposed computational tool delivers accurate predictions (average relative error 5%) for different geometries corresponding to real reactor set-ups. Extending the functionality beyond prediction, a computational experiment is performed to illuminate the interplay between species diffusion and chemical reaction rates, which determines the rate-limiting mechanism. The results indicate that species diffusion is fast enough and therefore reaction kinetics determine the overall deposition rate.

Aerosol based synthesis of highly conducting carbon nanotube macro assemblies by novel mist assisted precursor purging system

Taking hardware complexity into consideration of traditional continuous precursor purging systems for synthesis of few wall carbon nanotubes (CNTs) is a big challenge. Therefore, a novel precursor purging system for aerosol formation is designed to achieve uniform diameter distribution of CNTs, with the aerosol flow rate controlled either by number of ultrasonic mist makers or flow rate of carrier gas. Large droplets are turned into aerosol via an as-customized mist-producing system without the use of temperature or any chemical reaction. A built-in atomized gas valve is used to introduce the aerosol into a floating catalyst chemical vapour deposition (FCCVD) reactor. After an influential comparison of as-customized purging systems to the mostly used complex and big-budget systems for uniform diameter distribution, the quality of these CNT assemblies, synthesized using two different carrier gases (argon and hydrogen) is examined. Herein, CNT sheets with mostly fewer walls CNTs (diameter 2–10 nm) have been synthesized using this approach, with the controlled size of catalyst nanoparticles, under H2 atmosphere exhibiting low sulphur impurities, as evidenced by Raman, EDS, and XPS spectra, and have a fourteen-fold greater electrical conductivity (5.78 × 104S/m) than those synthesized under Ar atmosphere. Moreover, these sheets are also twisted and wrapped by insulating heat shrink tubes. The maximum current density of these conducting CNT wires having 250 µm diameter is 8.15 × 106A/m2. Further, one of the domestic applications of LED bulb (3–45 W) lightning is also demonstrated which shows the suitability of these conducting wires in numerous hi-profile applications.

Lowest Concentration of Chlorine Trifluoride Gas for Cleaning Silicon Carbide Chemical Vapor Deposition Reactor

A dilute chlorine trifluoride gas at less than 1% was possible for the cleaning of a silicon carbide chemical vapor deposition (CVD) reactor. For 20 min, the chlorine trifluoride gas at the concentrations of 0.5%–1% in ambient nitrogen at atmospheric pressure could detach the 30 μm-thick particle-type polycrystalline silicon carbide CVD film from the susceptor which had a coating film made of a purified pyrolytic carbon (PPyC). While the PPyC film had some damage due to the shallow fluorine diffusion, it could be recovered without any pit formation by annealing in ambient nitrogen containing a trace amount of oxygen at atmospheric pressure for 10 min at the temperature of 845 °C.

Chemical Vapor Deposition of Wide-Bandgap p-Type Semiconductor Cuprous Iodide for Optoelectronic Device Applications

Continuous, pinhole-free thin films of transparent conductive materials (TCMs) with p- and n-type conductivity are critical components of optoelectronic devices including photovoltaics (PV), transparent electronics, and LEDs [1]. TCMs with n-type conductivity are widely available in the form of semiconducting oxides [2]; however, p-type TCMs (hole transport materials, HTMs) with suitable conductivity are comparatively rare [1]. Particularly in the rapidly growing field of thin film perovskite PV, device-quality thin films of HTMs with high stability and conductivity are urgently needed to replace the organic HTMs typically employed in perovskite PV research [3]. As such, techniques to deposit inorganic HTM thin films are desired.With a focus on applying HTMs in optoelectronic devices at the commercial scale, these materials must be deposited by a scalable technique yielding thin, continuous, pinhole-free films. Chemical vapor deposition (CVD) is a highly scalable thin film deposition technique widely used in industry, with a proven ability to yield high-quality thin films on large-area substrates [4]. A variety of n-type TCMs are accessible by CVD techniques, but few CVD methods exist for p-type TCMs; examples include atomic layer deposition of NiOx and VOx [5].The cuprous halides (CuX, X = Cl, Br, I), which are optically transparent p-type semiconductors with bandgaps ~3 eV, are promising inorganic HTM candidates. Cuprous iodide is of particular interest due to its low resistivity (~10-2 Ohm·cm), high hole concentration and mobility (~1019 cm-3 and ~1-10 cm2V-1s-1, respectively), and its valence band maximum position (ionization potential: 5.0-5.4 eV), which is well-aligned with common perovskite absorber materials [6]. While CuI crystallite arrays have been obtained by metal-organic CVD [7], CVD of continuous CuI thin films has only been achieved by a two-step vapor conversion process, requiring initial deposition of a copper chalcogen followed by vapor-phase conversion to the halide [6].Our group has recently published a CVD technique enabling direct deposition of continuous CuBr thin films via CVD reaction between hydrogen bromide and vinyltrimethylsilane(hexafluoroacetylacetonato)copper(I) [Cu(hfac)(vtms)] [8], and this technique has been extended to deposition of CuI. X-ray photoelectron spectroscopy indicates pure CuI films with an atomic ratio of approximately 1:1 Cu:I, and x-ray diffraction confirms deposition of γ-CuI. Similar to our observations for CuBr films, substrate identity has significant effects on CuI film continuity. Progress towards CVD of continuous CuI films on substrates of interest for practical application in optoelectronic devices will be discussed, with a particular focus on perovskite PV.[1] A. N. Fioretti and M. Morales-Masis, "Bridging the p-type transparent conductive materials gap: synthesis approaches for disperse valence band materials," J. Photon. Energy, 10, 042002 (2020).[2] M. Morales-Masis, S. De Wolf, R. Woods-Robinson, J. W. Ager, and C. Ballif, "Transparent Electrodes for Efficient Optoelectronics," Adv. Electron. Mater., 3, 1600529 (2017).[3] B. Gil, A. J. Yun, Y. Lee, J. Kim, B. Lee, and B. Park, "Recent Progress in Inorganic Hole Transport Materials for Efficient and Stable Perovskite Solar Cells," Electron. Mater. Lett., 15, 505 (2019).[4] R. Gordon, "Chemical Vapor Deposition of Coatings on Glass," J. Non-Cryst. Solids, 218, 81 (1997).[5] J. A. Raiford, S. T. Oyakhire, and S. F. Bent, "Applications of atomic layer deposition and chemical vapor deposition for perovskite solar cells," Energy Environ. Sci., 13, 1997 (2020).[6] R. Heasley, L. M. Davis, D. Chua, C. M. Chang, and R. G. Gordon, "Vapor Deposition of Transparent, p-Type Cuprous Iodide Via a Two-Step Conversion Process," ACS Appl. Energy Mater., 1, 6953 (2018).[7] V. Gottschalch, S. Blaurock, G. Benndorf, J. Lenzner, M. Grundmann, and H. Krautscheid, "Copper iodide synthesized by iodization of Cu-films and deposited using MOCVD," J. Cryst. Growth, 471, 21 (2017).[8] C. M. Chang, L. M. Davis, E. K. Spear, and R. G. Gordon, "Chemical Vapor Deposition of Transparent, p-Type Cuprous Bromide Thin Films," Chem. Mater., 33, 1426 (2021).

(Invited, Digital Presentation) Improved Reliability of 4H-SiC Metal-Oxide-Semiconductor Devices Utilising Atomic Layer Deposited Layers with Enhanced Interface Quality

A major component of reliability of Silicon Carbide (4H-SiC) power electronics are due to the gate dielectric. Specific aspects such as hysteresis, insulator lifetime, threshold voltage (VTH) instability and high leakage currents, remain an issue of paramount importance which hamper the uptake of 4H-SiC power MOSFETs.1 The oxide understood to have the most importance is coincidently the native oxide, SiO2, due to the suitable band offset to 4H-SiC. However, most of the SiO2/SiC interface problems, such as carbon clusters, H content and O vacancies, are directly related to the thermal oxidation process.2 Here, we show these issues can partially be avoided by using dielectric deposition instead.Atomic layer deposition (ALD) offers specific advantages such as very low deposition temperature, excellent process control and suitability for conformal deposition of gate oxides in trench structures.3 Deposited oxides still require a post-deposition anneal (PDA) in a nitrogen-containing ambient4 such as nitrous oxide (N2O) or nitric oxide (NO) [2] to passivate the defects within the stack and improve the as-deposited layer’s poor electrical quality. We present the excellent reliability performance of ALD-deposited SiO2 layers on SiC through fabrication of metal-oxide-semiconductor capacitors (MOSCAPs) and then using time-dependent dielectric breakdown (TDDB) characterisation. The distribution of interface parameters, as well as the results from TDDB, have been investigated as metrics of improvement following the N2O PDA process. For benchmarking, processes will be compared to thermally grown oxides4 and LPCVD-deposited dielectric layers to demonstrate the superior process quality.An active 10 µm thick epitaxial layer of 4 × 1015 cm-3 n-type doping is used in this study and grown on 100 mm diameter, 4° off-axis (0001) 4H-SiC wafers. Growth was performed using a 30 μm/hr growth and N2 as a dopant in an LPE ACiS M8 chemical vapour deposition (CVD) reactor. After an initial clean, a 1 µm thick field oxide was deposited and a window was opened via photolithography and reactive ion etching (RIE). Then, quarter wafers underwent one of the three oxidation routines: 1. SiO2 plasma deposition at 200 °C using bis(diethylamino)silane (BDEAS) and O2 plasma precursors in an Ultratech Fiji G2 Plasma-Enhanced ALD System. 2. SiO2 deposition at 750 °C using tetraethyl orthosilicate (TEOS) as a precursor in a Thermco LPCVD system. 3. direct thermal growth of SiO2 in a HiTech furnace at 1300 °C for 5 hrs in N2O ambient. Samples that had undergone one of the first two routines then underwent a PDA in N2O, in the HiTech furnace at 1300°C for 2 hrs. All oxidation measurements resulted in oxide thicknesses between 50 and 60 nm, which were verified using step-height AFM measurements and optical interferometry. To create the vertical MOSCAP structure samples had a 500 nm aluminium (Al) backside contact deposited, before a 1 μm Al layer was deposited on the topside of the samples by means of a liftoff process. A cross-sectional diagram of the fabricated final device structure is shown in Fig. 1 (a). Table I shows the key electrical parameters which were extracted using room temperature C-V measurements, combined with I-V and constant field TDDB measurements at 175 °C. Fig. 1 (b) shows the improvement brought about by the N2O anneal, which also results in the average flatband voltage being reduced by more than 10 V to the lowest value of the dataset (1.44 V) and frequency dispersion mostly removed, with all but the ALD as-deposited samples reaching average breakdown oxide fields of about 10 MV/cm. The most promising improvement of the ALD-deposited SiO2 can be seen observing the breakdown distribution of MOSCAPs when stressed at constant high electric field (9 MV/cm), which can be seen in Fig. 2 (a) and (b). Here, these samples reach a TDDB, 63% value of 4786 s, which represents an average increase of 28% when compared to LPCVD samples and 58% when comparing this to a purely thermal process.Further evidence will be presented that high-quality, high-reliability SiO2 layers, formed by ALD and PDA have been formed. Flatband voltage and hysteresis are reduced, compared to thermally grown oxide, and frequency dispersion in accumulation is negligible. The ALD oxide with PDA has higher reliability than LPCVD and thermal oxides in TDDB tests, offering 29% to 345% improvement. The degradation mechanisms of the ALD oxide are different to that the LPCVD and thermal oxides and will be discussed in this talk.[1] P. Moens et al, ISPSD 32, 78-71 (2020).[2] P. Fiorenza et al, Appl. Surf. Sci., 149752 (2021).[3] A. Renz et al, MSSP 122, 105527 (2021).[4] K. Tachiki et al, Appl. Phy. Expr. 13.12, 121002(2020). Figure 1

Centimeter-Scale MoS2 Thin Films As a Temperature Sensor

Backgrounds/Introduction Transition-metal dichalcogenides (TMDs) is an atomically-thin semiconducting material family, exhibiting unique physical and multi-functional properties. Despite the great promises in flexible electronics, the practical adoption of TMDs in a wider variety of far-reaching application domains, including high-temperature applications such as automobiles and aircrafts, still requires TMDs to be prepared at a larger scale and tailor-researched to the needs of a specific application. In this work, molybdenum disulfide (MoS2), one of the most widely studied TMD materials, is synthesized at a centimeter-scale by sulfurizing the transition metal seed layer (Mo) in a CVD (chemical vapor deposition) reactor, and comprehensively characterized to explore MoS2’s potential as the next-generation temperature sensor. Key Results: Fig. 1 depicts both the schematic drawing (1a) and the transmission electron microscope (TEM) image (1b) of few-layer MoS2 thin films grown on a SiO2/Si substrate by the CVD process described in our earlier work [1]. As seen in the figure, 2D MoS2 layers were successfully grown in a planar direction with their basal planes parallel to the growth substrates. The horizontal growth of few-layer MoS2 thin films (thicknesses of less than 5 nm) was achieved by precisely controlling the thickness of the metal seed layer (Mo).We first investigated the Raman characteristics of our centimeter-scale (2cm x 2cm), CVD-grown MoS2 thin films at varying temperatures (from 26°C to 206°C) in Fig. 2. It is clearly seen that both E2g (out-of-plane vibration modes at ~ 383 cm-1) and A1g (in-plane vibration modes at ~ 408 cm-1) characteristic peaks appeared in the temperature-dependent Raman measurement. Since these peak positions are known to be strongly dependent on materials or external parameters (e.g., thickness, mechanical strain, charge transfer), observing any notable change in the peak position at varying conditions can lead to discovery of MoS2’s novel functionality. The overall trend of red shift (i.e., decrease of Raman shift) with an increase in temperature observed in Fig. 3 is in good agreement with what has been already reported for an exfoliated single-layer MoS2 flake [2]. This has been attributed to either charge transfer from the substrate (doping effect) or compressive strain resulted from thermal expansion coefficient mismatch between MoS2 and the substrate.In order to further elucidate the physical mechanism while examining the potential of MoS2 to become a temperature sensor of the RTD (resistance temperature detector) type, we carefully measured the conductivity vs. temperature characteristics by using the temperature controller-attached probe station (Figs. 4 and 5). Firstly, a clear trend of increase in electrical conductivity with temperature indicates the semiconducting nature of our MoS2 thin films (Fig. 4). More importantly, Fig. 5 suggests that electronic transport in the temperature range of room temperature to about 300°C follows an Arrhenius behavior, implying a variable-range hopping mechanism [3]. Table 1 summarizes the temperature coefficient (cm-1/°C, measured from Raman) and the activation energy (eV, measured from the Arrhenius plot). Significance: Previously, researchers have studied the temperature dependence of electrical conductivity for exfoliated MoS2 flakes (either undoped [4] or doped [5]). These methods may not be best suited for temperature sensing applications because of the small areal size and lack of tight control on the thickness. This work significantly advances the field by demonstrating the temperature-induced modulation of spectroscopic and electrical transport characteristics of a relatively large-area MoS2 thin film.

Lab-scale chemical vapor deposition onto powders

In this paper, a laboratory chemical vapor deposition (CVD) reactor is described, which features an opposing screw rotating fluidized bed. The reactor efficiently concentrates powdered reactants in the reaction zone while maintaining fluidization independent of powder properties. This allows for lab-scale CVD processing of many small powder samples at high yields and without the need for re-adjustment of fluidization parameters for different samples. Alumina and graphite were carbon-coated and characterized in lithium batteries. The deposited carbon layer had a density of 1.84 g/ml and a capacity of 225 mA h/g when cycled between 7 mV and 0.9 V in lithium cells. Carbon coatings applied by this CVD reactor onto graphite particles were found to be effective at reducing surface reactions during cycling in lithium cells. We suggest that utilization of this opposing screw rotating fluidized bed reactor can effectively apply CVD coatings to small laboratory powder samples, with particular utility for Li-ion battery materials.

Effects of indium composition on the surface morphological and optical properties of InGaN/GaN heterostructures

PurposeThis study aims to investigate the effects of indium composition on surface morphology and optical properties of indium gallium nitride on gallium nitride (InGaN/GaN) heterostructures.Design/methodology/approachThe InGaN/GaN heterostructures were grown on flat sapphire substrates using a metal-organic chemical vapour deposition reactor with a trimethylindium flow rate of 368 sccm. The indium composition of the InGaN epilayers was controlled by applying different substrate temperatures. The surface morphology and topography were observed using field emission scanning electron microscope (F.E.I. Nova NanoSEM 450) and atomic force microscopy (Bruker Dimension Edge) with a scanning area of 10 µm × 10 µm, respectively. The compositional analysis was done by Energy Dispersive X-Ray Analysis. Finally, the ultraviolet-visible (UV-Vis) spectrophotometer (Agilent Technology Cary Series UV-Vis-near-infrared spectrometer) was measured from 200 nm to 1500 nm to investigate the optical properties of the samples.FindingsThe InGaN/GaN thin films have been successfully grown at three different substrate temperatures. The indium composition reduced as the temperature increased. At 760 C, the highest indium composition was obtained, 21.17%. This result was acquired from the simulation fitting of ω−2θ scan on (0002) plane using LEPTOS software by Bruker D8 Discover. The InGaN/GaN shows significantly different surface morphologies and topographies as the indium composition increases. The thickness of InGaN epilayers of the structure was ∼300 nm estimated from the field emission scanning electron microscopy. The energy bandgap of the InGaN was 2.54 eV – 2.79 eV measured by UV-Vis measurements.Originality/valueIt can be seen from this work that changes in substrate temperature can affect the indium composition. From all the results obtained, this work can be helpful towards efficiency improvement in solar cell applications.

Utilization of catalytically active metals in mining waste and water for synthesis of carbon nanotubes

This study presents the application of fine-grained precipitates from mine waters for the synthesis of carbon nanotubes. Experimental synthesis of carbon nanotubes was carried out on natural substrates taken from the Slovak mining localities Markušovce, Smolník and Poproč. The substrates were obtained from mining waste taken from the shore dark sediment settling ponds in Markušovce, from the water flowing out of the mine in Smolník and from the sediment collected from the mine of Poproč. The main components of the colloidal residues resulting from the extraction of ores are particles containing catalytically active metals. Microscopic analysis of nanocomposites synthetized in a hot filament chemical vapour deposition reactor shows that the sediments from all residues after ore mining have a high ability to catalyse the synthesis of carbon nanotubes. The combination of catalyst particles and co-catalyst plays an essential role in the formation of carbon nanotubes. • Precipitates from mining waste and water were used for catalyst preparation. • Colloidal residues are particles containing catalytically active metals. • Catalytically active metals are used for synthesis of carbon nanotubes and for nanocomposite formation by CVD technique. • Combination of catalyst particles and co-catalyst plays an essential role in the formation of carbon nanotubes and nanofibers.